How do I put an image texture on a material in Cycles?
Applying an Image Texture in Cycles


Select the object you want to put the image on
Give it a new material with an Image Texture Shader:
Object Properties window -> Materials tab -> click the New button
For the Color, click on the grey dot icon on the right side (  ) then select "Image Texture":

  
Select the image you want to use:  


UV Unwrap your object and position the image as you'd like it:  


Select your object and enter Edit mode (TAB)
Unwrap mesh (U) -> here, I use Smart UV project




NOTE: UV Unwrapping a mesh and positioning the image properly can be a very complex and involved process. So, I highly recommend you study some UV Mapping tutorials to get all the details; YouTube has quite a lot of excellent video tutorials for beginners on this subject.